A central objective of the project has been and continues to be the preparation of synthetic lipid membranes containing membrane-bound haptens (especially spin-label nitroxides) as well as other functional antigenic molecules, such as components of the H-2 complex. A second objective has been and continues to be the determination of the lateral mobilities and distributions of haptens and molecules in reconstituted membranes. A third objective is to determine if there is a quantitative and understandable relationship between these lateral distributions, lateral mobilities, and (a) the susceptibility of hapten-sensitized vesicles to complement-mediated and lymphocyte-mediated attack, and (b) the degree to which such vesicles can direct immune responses in vitro and in vivo. As discussed below, progress in achieving the above objectives has been so great that we are now beginning to concentrate on the inclusion of H-2 components in model membranes, in order to study their function in cell-mediated cytotoxicity.